The Radio Resource Management (RRM) e.g. in the GERAN (GSM/EDGE Radio Access Network; GSM, Global System for Mobile Communications; EDGE, Enhanced Data rates for GSM Evolution) and the UTRAN (UMTS Terrestrial Radio Access Network) are responsible for utilisation of air interface resources. The RRM is needed for e.g. maintaining the QoS (Quality of Service), planned coverage, and for offering high capacity. The RRM enables optimising service capacity and capability. The full scope of the RRM is large, and several algorithms are needed to perform various tasks. These algorithms include also Admission Control (AC).
The purpose of admission control is to ensure that there are free radio resources for the intended call or session with required signal-to-interference ratio (SIR) and bit rate. Admission control is always performed when a mobile station initiates communications in a new cell, either through a new call or handover. Furthermore, admission control is performed when a new service is added during an active call. In general, the admission control procedure ensures that the interference created after adding a new call does not exceed a prespecified threshold.
Admission control needs to be done separately for uplink and downlink direction. This is especially important if the traffic is highly asymmetric. Typical criteria for admission control are call blocking and call dropping. Blocking occurs when a new user is denied access to the system. Call dropping means that a call of an existing user is terminated. Call dropping is typically considered to be more annoying than blocking.
If the air interface load is allowed to increase excessively, the coverage area of the cell is reduced below the planned values, and the quality of service (QoS) of the existing connections cannot be guaranteed. The QoS is the idea that transmission rates, error rates, delay, and other characteristics that can be measured, improved, and, to some extent, guaranteed in advance. The QoS is of particular concern for the continuous transmission of video and multimedia information. Transmitting this kind of content dependably is difficult in public networks using ordinary “best effort” protocols. Before admitting a new connection, the admission control needs to check that the admittance will not sacrifice the planned coverage area or the quality of the existing connections. Admission control accepts or rejects a request for establishing a radio access bearer in the radio access network. The admission control functionality is located in the Radio Access Node (RNC) in the Universal Mobile Telecommunication System (UMTS) where the load information from several cells can be obtained. The admission control algorithm estimates the load increase that the establishment of the bearer would cause in the radio network. The requesting bearer can be admitted only if both uplink and downlink admission control admit it, otherwise it is rejected because of the excessive interference that is would be generated in the network. The limits for admission control are set by the radio network planning.
To support services that require some guarantees (e.g. multimedia streaming services) means that the radio access network (in the RNC and Base Station System (BSS)) needs to guarantee certain QoS in terms of throughput and delay. If some guarantees are needed, then radio resource reservation is required. Therefore, admission control can be used to calculate what network resources are required to provide the requested QoS, to determine if resources are available, and to reserve them.
During the connection the usage of radio resources are monitored by a Quality Control (QC) function, which makes sure that the provided QoS is in line with the negotiated ones, i.e. which tackles degraded situations to maintain the QoS for the most of the users at the expense of a few users' QoS. In case of real time (RT) traffic, if the target throughput cannot be achieved, QoS renegotiation might be necessary.
The main problem is that there is a need for different treatment in the admission control for streaming data flows sharing the same radio resources and experiencing different radio link conditions. The reason for that is that streaming connections are using shared Medium Access Control (MAC) mode, with the aim of increasing the resource utilisation, but at the same time these connections have real time requirements, such as guaranteed bitrate. Since determined radio link conditions lead to a determined experienced throughput, each connection needs to be managed separately to assure that the negotiated QoS requirements are fulfilled.